Lateral Gene Transfer and Metabolic Adaptation in the Human Parasite Trichomonas vaginalis

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Abstract
The evolution of a parasitic lifestyle necessitates adaptation to a specialized niche. Examples of common adaptive traits include host interaction systems, metabolic pathways that allow the acquisition of nutrients from the host, and mechanisms to evade host defenses. Such traits could originate by a process of gradual change, but there are mechanisms that would allow potential parasites to adapt very quickly, and one of these mechanisms is lateral gene transfer. Lateral transfer is the process by which genetic information is passed from one genome to an unrelated genome, where it is stably integrated and maintained. There is growing evidence from whole-genome analyses that this process is a very important mechanism in genome evolution, particularly among prokaryotes (Lawrence 1999 ). Lateral transfer may be especially important in the evolution of a parasitic lifestyle, as infection-related factors could be transmitted, and many of these factors would presumably confer an immediate selective advantage. In bacteria, there are many examples of adaptations that have been acquired through lateral gene transfer between pathogenic species; for instance, pathogenicity islands thought to be derived from a common ancestor are found in the genomes of many distantly related bacterial pathogens (Groisman and Ochman 1996 ).